1. Field of the Invention
This invention relates to an aircraft seat equipped with a self-adjusting shoulder harness that enables the position of the shoulder harness to be automatically adjusted in accordance with the seating height of the seat occupant.
2. Description of the Related Art
The seats of military aircraft are frequently equipped with restraint harnesses for restraining the occupants of the seats against forces experienced during operation of the aircraft. Since the forces which occur aboard a military aircraft during even normal operation can be quite significant, much research has gone into determining the ideal geometry of restraint harnesses for best protecting seat occupants.
Typical restraint harnesses include lap harnesses, which extend partly around the waist region of a seat occupant, and shoulder harnesses, which include one or more shoulder straps each extending over a shoulder of a seat occupant from behind his back to his front and a anti-g strap to prevent submarining. One such restraint system is described in U.S. Pat. No. 5,746,395 (the ""395 patent) that is directed to a helicopter seat safety system. The ""395 patent discloses a helicopter seat with a harness system. The harness system includes a strap tensioning device that is triggered to tighten the harness straps upon detection of a collision. However, the ""395 patent does not address the angular position of the straps with respect to the occupant.
Research on restraint systems has shown that the shoulder straps of a shoulder harness ideally should pass over the shoulders in a plane perpendicular to a line tangent to the back of the seat occupant or at an upward angle with respect to this plane of no greater than 30 degrees. If the shoulder straps pass over the shoulders at an angle below this plane, an undesirable force can be applied to the spine of the seat occupant during a sudden deceleration.
In a conventional seat for a military aircraft, the height of a shoulder harness on the seat is not readily adjustable by the seat occupant and is permanently set at a height appropriate for a seat occupant having a height falling in the 50th percentile of the population expected to be using the seat. As a result, for a tall or short seat occupant having a height significantly different from the height of the 50th percentile, the angle of the shoulder straps with respect to the back of the seat occupant can frequently fall outside of the above-described acceptable range, resulting in forces which are undesirable in magnitude or direction being applied to the back of the seat occupant during a sudden deceleration.
Accordingly, there is a need for an aircraft seat that is readily adjustable to safely accommodate occupants of differing heights.
The present invention provides a seat equipped with a shoulder harness that can be readily adjusted by a seat occupant to a position appropriate for the height of the seat occupant.
The present invention also provides a method of adjusting a shoulder harness for a seat.
According to one aspect of the present invention, a seat includes a seat back for supporting a back of a seat occupant and a shoulder harness including at least one shoulder strap for restraining a shoulder of a seat occupant. The shoulder strap has a rear portion anchored in a manner enabling it to move in a height direction of a seat occupant. When the seat occupant tightens the shoulder strap, the rear portion can move in response to the tension to a position in which the shoulder strap extends substantially perpendicular to the back tangent line of the seat occupant. In this manner the shoulder strap can be automatically adjusted in position for a wide range of seat occupants of varying heights. In a preferred embodiment, the shoulder strap is anchored on the seat back, but it may also be anchored on a bulkhead or other member supporting the seat. The shoulder harness may have a single shoulder strap, or it may have two shoulder straps, each anchored in a similar manner.
According to another aspect of the present invention, a method of adjusting a shoulder harness for a seat includes placing a shoulder strap of a shoulder harness for a seat over a shoulder of a seat occupant, and tightening the shoulder strap to exert a tensile force on a rear portion of the shoulder strap to move the rear portion in a height direction of the seat occupant. Preferably the rear portion can be moved to a position in which the shoulder strap is approximately perpendicular to a back tangent line of the seat occupant. The method can be performed by a seat occupant in the ordinary course of putting on the shoulder harness and requires no special training on the part of the seat occupant.
In a preferred embodiment, a seat according to the present invention is intended for use in an aircraft, but the seat may be used with any type of conveyance or moving object having a shoulder harness for restraining a seat occupant. For example, it can be used in trains, automobiles, boats, amusement park rides, spacecraft, and test equipment.